Electronic calibrating means for indicating instruments in pulse echo systems



Jan. 25, 1949. P. c. MICHEL 2,460,142

ELECTRONIC CALIBRATING MEANS FOR INDICATING INSTRUMENTS IN PULSE ECHO SYSTEMS Filed Jan. so, 1945 Fig. I. 4

Inventor: Philip 0. Michel, 7a a His Attorney.

Patented Jan. 25, 1949 ELECTRONIC CALIBRATING MEANS FOR INDICATING INSTRUMENTS IN PULSE ECHO SYSTEMS Philip 0. Michel, Schenectady, N. Y., asslgnor to General Electric Company, a corporation of New York Application January 30, 1945, Serial No. 576,567

7 Claims.

This invention relates to pulse echo systems and more particularly to means for calibrating certain of the indicating devices in such systems.

Pulse echo systems have been proposed for the determination of the range and relative velocity of a desired object. Such systems are useful on moving objects, such as aircraft and ships, for studying the relative motion of other moving objects, or for indicating the approach of a moving object to a fixed object. Thus, it may be desired to determine the relative speed between relatively nearby aircraft and also to determine whether the distance between them is becoming less or greater. For the satisfactory operation of such systems, it is necessary to have available testing equipment for calibrating accurately the indicating instruments associated with the pulse echo system.

It is an object of my invention to provide calibrating or testing equipment capable of checking either the range or relative velocity indicators, or both, in pulse echo systems.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. l is a schematic diagram of the circuits constituting one embodiment of my invention, and Figs. 2 to 5 inclusive are diagrams illustrating operating characteristics of the circuit illustrated in Fig. 1.

In accordance with my invention, there is provided calibrating apparatus which provides an artificial target pulse which can be made to move over a wide range of relative distances at a Wide range of relative velocities with respect to an external input synchronizing pulse derived from the pulse echo system being calibrated.

Referring to Fig. 1 of the drawing, there is provided a fast sweep generator 5 arranged to generate a timing wave at a recurrence rate of the order of microseconds. There is also provided gating means 2 for initiating operation of the fast sweep generator in response to suitable synchronizing pulses received from the pulse echo system. The voltage obtained from the fast sweep generator is impressed upon a trigger device 3 which in turn triggers a suitable pulsiing device 4. The artificial target pulses emitted from the pulser are impressed on the pulse echo system to be calibrated.

The circuit shown in Fig. 1 is designed to cali-. brate velocities at two levels. The absolute values of the velocities will depend upon the values of the various components of the circuit. In the particular example illustrated herein, the velocities are of the order of and 500 miles per hour away from or toward the reference point which in practical operation is the side of the pulse echo equipment. In order to choose the approximate rate and direction of travel there is provided a two arm switch 5 having plus and minus 100 miles per hour positions and plus and minus 500' miles per hourpositions, ,the terms plus and minus referring to the relative approach and recession, respectively, of the ob.- jects involved. The position of switch 5 determines the maximum velocity to be calibrated. In order to select a lower velocity than the maximum, there is provided a fractional velocity multiplier or control 6 shown in theform of a potentiometer. When the arm of the. potentiometer engages one end of the resistance the velocity is minimum and when the arm is at the other end of the resistance the velocity is the maximum for the setting of switch 5. In operation, assuming power is suitably connected to the circuit, and output leads 8 and input lead 9 are suitably connected to the equipment to be tested, the relative velocity control Eris turned to the desired position. For purposes lof description, let it be assumed that the switch 5 is turned to the plus 500 miles per hour position as indicated in Fig. 1. The velocity multiplier potentiometer 6 is set to a position corresponding to the absolute velocity to be calibrated as, for example, 350 miles per hour. There is provided an initial range control H] which is operated until the pulse echo equipment being calibrated locks on the artificial target pulse from the pulsing device 4. Under these conditions the range indicator of the pulse echo equipment now varies as the range of the artificial target changes.

Hold down switch II is then pressed, making operative the slow sweep generator to modify the bias or threshhold of the trigger device 3. By reason of changing bias during the operative period of the second sweep generator 1, as hereinafter explained, the target indicationwill move in the selected direction (toward the operator for conditions as illustrated in Fig. 1) at a selected rateidetermined by the relative. velocity switch 5 and velocitymultiplier potentiometer 6). Describing 'rnyinventionin greater detail, the

fast sweepgenerator l includes an electron discharge device illustrated as being of the pentode type having an anode it, a cathode 53, control electrode M, screen grid electrode 15 and suppressor grid 16. The anode 1215 connected to a suitablessource' of positive potentiahthe negative terminal of said source being grounded. The screen electrode i5 is connected to a suitable source of potential through a suitable voltage limiting resistor ll. The cathode liiis connected to the upper end of a cathodeihias resistor i3. The suppressor grid i6 and control electrode H! are connected together andto the lower end of resistor I8. In order to maintain relativelyconstant the potential on screen electrode ill with respect to the cathode. there is provided a capacitor 19 connected betweenthe"screeirel'ectrode l5 and the lower end of resistor 18. In series with the above-described electron discharge device, there is a second electron discharge device it! which may be a suitable double-'triode typehaving anodes 2i and 22, contror'el'ectro-des'25 and 26 and cathodes "25 and 28 respectively. The cathode'l'3. is connected tothe anode 22 through the bias resistor' i8and'the initial range control it including potentiometer 21 The cathodes 25 and "2 6 areponnecte'dtogether'and to ground through abias resistor 28. The control electrode 24 is connected to' the anode"? l through a suitable capacitor'29. The'two sides of theclectron discharge device "at are connectedtogether for multivibrator' operation with the right hand side normally conducting-and the left hand sidenormallycut off. When a sufilcientlypositive synchronizing pulse from the pulse echo "system is impressed upon the control electrode "23, as y meansrof'a suitable-coupling capacitor 39; multivi'brator action quickly renders the left-side conductive' and the right side of' electron discharge device 28 non-conductive, the control electrode 24 having beendriven sulficiently negative to out 'off' the-discharge current.

The relative v'elocityswitc-ht comprises apair ofswitchelements 3i and 32'having switch arms arrangedto'engage a plurality of contacts as in- "dicated in *the drawing. -As briefly explained hertofore there are four switch positions. The "firstiposition representsa negative velocity of SBCt-znilespexhourgthe second position'represents a'negatrverate or 10% milesper-houu'the third *position represents a "positiverate of 100 miles per hour and theffourth'position (indicated in the drawing) 'represents'a positive rate of 500 "milesiper'hour. The switch arm of'switch ele menttl is connected to a suitablesourceof 1105i" tive potential and also to one side ofcapacitors 3'3 and. "The negative and'positivefifil) milesper hour contacts ofswitchelement- 3! are connected together'and to'one side of capacitor 35. The

other sides of capacitors 33, Stand 35 are 'connected together and to anodeflz and the lower terminal of "potentiometer 2?. Thusxwhen the relative velocity switchc is niche of the 500 miles per hourpositionsall' three capacito s are'connecte'd' in parallel to the source ofpositivepotential whereas in the loll-miles perhour position of the "switch "only'capacitors 33, and Mare connectedto the source of potential.

When the'right' hand 'si'depfdischarge device Zllisconducting, thecapacitors connected in the circuit become charged. Atthe instant that discharge device 2011s cut ofiythe lower sides of capacitors33 "andc' (and capacitor 35* in either of the *500 "miles 'per hour positions) are attthe potential of 'the positive source and the upper graphically in Fig. 2. 'trated from conductor 8.

ethic bias resistor 4 sides of the capacitors are at the potential of anode 22. While the right hand side of discharge device 2% is cut off, the potential. of the upper sides of the capacitors rises substantially linearly tothat of the lower side. That is the condenser 33 and 3 discharge.

The action thus far described indicated At line A there are illuspositive synchronizing Line B represents the potential at the upper sides i the cap citors 33 and 34 and hence, at the anode 22 of discharge device 28. When the right side or" discharge device-Z0. again becomes conductive, the potential at the upper sides of he capacitors fails to its normal value and the sweep genera and gating means are conditioned for the next synchronizing pulse.

The trigger device 3 comprises an electron discharge device 35 of a suitable double triode type although two separate suitable electron discharge devices maybe used. The right hand side acts as a cathode follower and normally conducts current of magnitude depending upon the potential appearing at the control electrode potential is determined by the setting of the relative velocity switch 5. The anode is connected to suitable source of positive potential. The cathode 39 is connected to ground throng suit- The cathode ii of the left a d or trigger side of the dis'harge device 35 is .zected to cathode and upper end of resistor 69. The anode $2 is connected to the pulsing device t. The control electrode 33 is representative connected to the arm of the potentiometer through a suitable potential limiting resistor. In order to minimize the effect of the gridwathode capacity in the left hand side of discharge device 35, a suitable capacitor M is connected between -anode 22 and control electrode t3.

As the potential at the lower end of potentiometer 27 increases, the potential at the control electrode 53 increases proportionately. Even tually, depending upon the bias established for the trigger device, the left hand side of device 35 conducts current. Thus, at a certain delay time after the synchronizing pulse is applied to control electrode 23 of discharge device a time interval depending upon the setting of the potentiometer lfl and the" bias of left side discharge device 36, a trigger pulse appears on anode 32 indicated at line C in Fig. 2 which results in the emission of an artificial target pu from the pulser i as indicated at line D in 2.

The apparatus thus far ascribed is sufficient to calibrate the range incicatcr of pulse echo system. For example, a range within the limits of the pulse echo system and the calibrating device is selected by properly adjusting potentiometer 2i. Assumingconnection of the calibration device to the pulse echo system, the artificial target pulse should appear at the chosen range mark on the pulse echo equipment. In order to check different ranges, it .is simply necessary to change the setting of poten iorneter 2?. In a typical embodiment of this circuit, capacitors 33, (i l and 35 are so chosen that the range coverage with switch in the 106 miles per hour setting is approximately 480 to coco yards in the other isfactory results are obtained if several condens- "r5'ers"are used'because'of improved accuracy obtained, and minimum voltage source requirements.

In order to calibrate that portion of the pulse echo system used for checking the relative velocities of moving objects, there is provided means for continuously, and preferably linearly, varying the threshold on the trigger side of discharge device 36 in either the positive or negative direction. For this purpose, there is provided the slow sweep generator 1 having a period of recurrence of the order of seconds (it will be recalled that the period of recurrence of the fast sweep generator is of the order of microseconds). The voltage derived from the slow sweep generator is applied to the control electrode 3'5 of electron discharge device 36. Any change in the bias of control electrode 31 varies the current through the resistor 4G and hence the threshold of the left hand side of electron discharge device 36. Accordingly, it will take a shorter or longer time for the linearly increasing voltage applied to control electrode 43 to overcome the threshold depending upon the direction in which the potential of control electrode 31 is changing.

The illustrated slow sweep generator 7 includes an electron discharge device 45 which may be of a suitable double triode type. The anode 5$ of the right hand side is connected to a suitable source of positive potential through the positive range set control 63 illustrated in the form of a variable resistor. The cathode 51 is connected to ground through a suitable bias resistor 48. The control electrode is is connected to ground through a resistor 55 and normally closed hold down switch H. A suitable capacitor 5! is connected between anode 46 and the junction between resistor 55: and hold down switch H. The junction between hold down switch 3 l and capacitor 5! is connected to a suitable source of positive potential. With this arrangement, the control electrode 49 is normally grounded through the switch II. When it is desired to initiate operation of the slow sweep generator, hold down switch II is pressed thereby opening the circuit from grid to ground. As soon as the switch I! is opened the lower side of capacitor 5| is released from ground and the capacitor 5| begins to discharge substantially linearly until the switch is released, thereby again grounding the capacitor, or until grid current flows in the right hand side of discharge device 45. The potential on control electrode 49 follows the voltage on the lower side of capacitor 5| so that as this voltage increases linearly, the current flow through the right hand side of discharge device r 65 increases proportionately. As a result, the potential of anode 46 decreases linearly and therefore a linearly decreasing voltage appears fore, the decreasing voltage causes the potential on control electrode 37 of discharge device 36 to decrease whenever the switch 32 is engaging the positive rate contacts. As a result, with switch 5 in the position shown, the current through the cathode follower side of discharge device 35 decreases, the current through resistor 45.- decreases and the threshold on the left hand or trigger side of discharge devicetfi also decreases continuously and substantially linearly.

Therefore, the trigger side triggers continuously faster, that is, after shorter and shorter intervals, as long as the hold down switch H is held open or until grid current flows in the right hand side of discharge device 45.

Fig. 3 represents the effect of holding open the switch H for different lengths of time. In a' typical embodiment of my invention approximately 40 seconds is required to cause grid current to flow in the right hand side of discharge device iii. The full. line in Fig. 3 is representative of the condition where the switch l l is held open for 30 seconds. If the switch is held open only 15 seconds, the charging voltage follows the same line but halts sooner and at a lower maximum amplitude as indicated by the dashed line. In Fig. 4 the line 53 represents the continuously and linearly decreasing voltage appearing at control electrode 37.

The anode 5-5 of the left hand or phase inverter side of discharge device 35 is connected to a suitable source of positive potential and to the negative switch contacts of switch element 32 through a suitable voltage limiting resistor. The cathode 55 is connected to ground through a suitable bias resistor 55. As the voltage on control electrode 52 decreases, as explained above, the current through the left hand side of discharge device ifi decreases whereby the potential of anode 55 increases continuously and substantially linearly as indicated by the line 51 in Fig. 4. Whenever the switch arm of switch element 32 is turned to a position in which the switch arm engages either of the negative rate contacts, the potential on control electrode 37 will continuously and linearly increase in the positive direction, when switch I l is opened, causing a continuous increase in current through the right hand side of discharge device 36, a continuous increase in current through resistor ill and therefore a continuous substantially linear increase in the threshold of the left hand side of the discharge device 36 and so, as time goes on, an increasingly higher voltage is required from the initial range control potentiometer 2'! to cause triggering of the pulser. The result is that the device 36 triggers after longer and longer intervals.

Hence the time intervals after reception of pulses on condenser 9 when device 35 triggers device 4 increase or decrease at a uniform rate in accordance with the direction of change or relative potential of the potential impressed on the control electrode 3'! of the right hand side of discharge device 35 and therefore in accordance with the direction in and extent to which the threshold is modified when the slow sweep generator is operative. Fig. 5 depicts graphically the variation in trigger time of the discharge de-- vice 36. Time relationships have been distorted to illustrate clearly operating characteristics. The line 58 represents the sweep voltage applied to control electrode 123 as a result of the operation of the fast sweep generator and gating means. The line 59 represents a gradually increasing threshold at the left hand side of discharge device 36. Line fill represents the nor mal threshold or cut-off bias on the left hand side of discharge device 35. Line 6| represents the resulting variation of potential on control electrode d3 of discharge device 36. Whenever the resultant effective control electrode potential crosses the cut-oil line, represented by the numeral '65, the trigger device is rendered operative. It will be noted that as time passes, the interval between successive periods of energization-zofthe. left handrsideof device 36, .as indicate'cljby A and B in Fig. 5, becomes less and less. Iiithe switch is in orient the negative rate pcs1 tions, a similar analysis wculd show triggering at greater and greater intervals as the hold down switch is'operated.

,"Means is provided to make the initial range of the artificial target pulses independent of the setting of velocity multiplier 6. That is, with switch H closed variation of the position of the movable contact on potentiometer EE- should not aifect the potential on grid ill of device 3'5 or the bias voltage on resistance ill irrespective of the position of switch This is accomplished by adjusting the voltage on the anode to the samev amplitude as that on the lower end ofthe velocity-multiplier 6. With such an arrangement, variation of the arm of potentiometer 6 will not upset the voltage relationships on the left hand side of discharge device 45 and the starting potential, i. e. the potential when switch I l is first opened, on the movable arm of velocity multiplier i will always be equal to the potential on anode 36, assuming proper adjustment of resistor 63.

In'order to provide, at any given range, the samerateof change of relative velocities for approach and recession tests, there is provided an adjustable resistance 52 connected'between the negative contacts of the'switch element 32 and the :arm of the potentiometer comprising the 'negative'rate range set control The same starting voltage at switch 5 may be obtained for the positive and negative directions of relative velocity by changing the negative rate range set control (i i. In other words, the starting voltage on the negative rate contacts of switch element 32' is determined by the setting of potentiometer E l negative rate calibration resi'tance 52. The starting voltage on the positive contacts of the switch element 32 depends upon the setting oithe resistor 53 and the velocity multiplier 5, assuming that the'voltage across controls has been'properly adjusted to zero.

Inorder to compensate for the different cathode currents obtained in resistor 28 of gating means 2 in the 10b and 500 miles per hour positions. of switch 5 and provide equal bias for the left hand. side of device 28 in all positions of switch 5, there is connected between cathode 2 and the lower end of capacitor 35' a suitable resistor 65. This resistance 65 passes current from the positive terminal of the source of operating potential to ground through resistance 28 to produce increased bias thereon when switch 5 is in those of its positions where the bias on this resistance produced by current flowing through tube is smaller. The bias on resistance 23 is produced in part at least by current flowing in grid 2 and through the diflerent grid resistors to the positive terminal of the source of operating potential. These resistors have values chosen in accord with the desired rates of variation of the rise in voltage represented by curve B. Since they are unequal, unequal currents flow in the when switch 5 is in difierent positions. 'Rc sistance is chosen to make the bias on resistance 23 equal in all positions of the switc notwithstanding the unequality of the current flowing in tube for different positions of the switch.

The complete calibrating system, the fast sweep generator .andcertain aspects of the slow sweep generator are shown, described and claimed the copending application of.Don ML-Jacob,

Efa

Serial-No. 5'75,-309, -fi1ed of evendate, and-v assigned to the same assignee as the present invention,

WhileI have shown-and described a particular embodiment of my invention, it will be.ob-. vious to those skilled in the art that changes and modifications may be 'made without departing from my invention in its broadest aspects, and I therefore aim in the appended claims to cover all suchchanges and modifications as fall within the true spirit and scope of my invention.

What Iclaim as new and desire to secureby Letters Patent of the United States, is:

1. The combination, in a systen'rfor producing pulses simulating echoes from a remote moving object of recurrent pulses transmlttedto said moving object, of means to produce pulses simulating echoes, each echo simulating pulse being produced aftera'predetermined interval followlng a corresponding one of said recurrent. pulses, means to increase or decrease said intervals following successive ones of said recurrent pulses thereby to cause said successive echo simulating pulses to occur at times after the corresponding recurrent pulses corresponding to a movement of said object directions of increased or decreased range respectively and :common' adjustment means for adjusting the rate of said increase and decrease of said intervals.

2. The combination, in a system for producing pulses simulating echoes from a remote moving object of recurrent pulses transmittedto said moving object, of means to produce pulses simulating echoes, each echo simulating'pulse being 7 produced after a predetermined interval following a corresponding one of said reccurent'pulses,

lating echoes, each echo simulating pulse being produced after a predetermined interval'following a corresponding one of said recurrent pulses, and means to increase or decrease said intervals following successive ones of said recurrent pulses thereby to cause said successive echo simulating pulsestonoccur at times after the corresponding recurrent pulses corresponding to a movement of said object in directions of increasedor decreased range respectively, common adjustment means for adjusting the rate of said increase and decrease of said intervals, means to initiate action of said interval increase and decrease means, and means to prevent adjustment of'said common adjustment means from affecting the interval between said recurrent pulsesand the corresponding echo simulating pulses occurring at the instant of initiation of action of said echo increase and decrease means by said action initiating means.

4. The combination, in a system for producing pulses simulating echoes from a remote moving object of recurrent pulses transmitted thereto, means to produce a unidirectional :voltage varying with time, means to'control the l'ntervals'betweenthe difierent recurrent pulses and the. next echo simulating pulse in accord with said voltage, said last means comprising an electron discharge device having an anode, a cathode and a control electrode, a source of operating potential, said cathode being connected to the negative terminal of said source, a resistance connected between said anode and the positive terminal of said source, a condenser between said anode and control electrode, a switch between said control electrode and cathode, said control electrode being connected to the positive terminal of said source, a potentiometer connected between said anode and a point of fixed potential equal to the potential of said anode when said switch is closed whereby when said switch is opened the charge in said condenser varies thereby varying the potential on said control electrode, and means to vary said unidirectional voltage in accord with the potential on said potentiometer.

5. The combination, in a system for producing pulses simulating echoes from a remote moving object of recurrent pulses transmitted thereto, means to produce a unidirectional voltage, means to control the duration of the interval between each recurrent pulse and the next echo simulating pulse in accord with said voltage, said last means comprising a pair of electron discharge devices and a source of operating potential, each discharge device having an anode, a control electrode, and a cathode, said cathode being connected to the negative terminal of said source and said anodes being connected through respective resistors to the positive terminal of said source, a condenser connected between the control electrode and anode of one of said devices, a switch connected between said last control electrode and a point of fixed potential, and a potentiometer connected between the anode of said one device and a point of fixed potental equal to the potential of said last anode when said switch is closed whereby when said switch is opened the potential across said potentiometer increases at at rate corresponding to the rate of change in charge in said condenser, means to supply potential from said potentiometer to said control electrode of said other device, and means to derive said voltage either from said potentiometer or from the anode of said other device, whereby the time intervals between said recurrent pulses and said echo simulating pulses increase or decrease when said switch is open from a duration independent of the adjustment of said potentiometer and at a rate determined by said condenser and the adjustment of said potentiometer.

6. The combination, in a system for producing pulses simulating echoes from a remote moving object of recurrent pulses transmitted thereto, means to produce a unidirectional voltage, means to control the duration of the interval between each recurrent pulse and the next echo simulating pulse in accord with said voltage, said last means comprising a pair of electron discharge devices and a source of operating potential, each discharge device having an anode, a control electrode, and a cathode, said cathodes being connected to the negative terminal of said source and said anodes being connected through respective resistors to the positive terminal of said source, a condenser connected between the control electrode and anode of one of said devices, a switch connected between said last control electrode and a point of fixed potential, and a potentiometer connected between the anode of said one device and a point of fixed potential equal to the potential of said last anode when said switch is closed whereby when said switch is opened the potential across said potentiometer increases at a rate corresponding to the rate of change in charge in said condenser, means to supply potential fromsaid potentiometer to said control electrode of said other devices, and means to derive said voltage either from said potentiometer or from the anode of said other device, whereby the time intervals between said recurrent pulses and said echo simulating pulses increase or decrease when said switch is open from a duration independent of the adjustment of said potentiometer and at a rate determined by said condenser and the adjustment of said potentiometer and means to equalize the rates of change in potentials derived by said last means.

'7. The combination, in a system for producing pulses simulating echoes from a remote moving object of recurrent pulses transmitted thereto, means to produce a unidirectional voltage, means to control the duration of the interval between each recurrent pulse and the next echo simulating pulse in accord with said voltage, said last means comprising a pair of electron discharge devices and a source of operating potential, each discharge device having an anode, a control electrode, and a cathode, said cathodes being connected to the negative terminal of said source and said anodes being connected through respective resistors to the positive terminal of said source, a condenser connected between the control electrode and mode of one of said devices, a switch connected between said last control electrode and a point of fixed potential, and a potentiometer connected between the anode of said one device and a point of fixed potential equal to the potential of said last anode when said switch is closed whereby when said switch is opened the potential across said potentiometer increases at a rate corresponding to the rate of change in charge in said condenser, means to supply potential from said potentiometer to said control electrode of said other devices, and means to derive said voltage either from said potentiometer or from the anode of said other device, whereby the time intervals between said recurrent pulses and said echo simulating pulses increase or decrease when said switch is open from a duration independent of the adjustment of said potentiometer and at a rate determined by said condenser and the adjustment of said potentiometer, and means to adjust the potentials derived by said last means when said switch is initially opened to equal values and to equalize the rates of change of said derived potentials.

PHILIP C. MICHEL.

REFERENCES CITED ihe following references are of record in the his or this patent:

UNITED STATES PATENTS Number Name Date 2,188,580 Schlesinger -i Jan. 30, 1940 2,208,254 Geohegan July 16, 1940 2,264,197 Hadfield Nov. 25, 1941 

